The present invention relates to apparatus and methods for improving cellular communication networks. More particularly, the present invention relates to improved base transceiver stations (BTS) architectures in a cellular communication network.
Cellular communication systems are well known in the art. In a typical cellular communication, the mobile stations (MS's) may transmit and receive voice and/or data with the cellular network and one another utilizing radio waves. To facilitate discussion, FIG. 1 depicts the architecture of a cellular communication network 100 that implements the well-known Global System for Mobile Communication (GSM) standard. Although the GSM cellular network is chosen herein for illustration purposes, it should be borne in mind that the invention disclosed herein is not limited to any particular standard.
In FIG. 1, there is shown a plurality of mobile stations (MS's) 102, 104, and 106, representing the mobile interface with the cellular users. In a typical network, MS's 102, 104 and 106 may be, for example, the mobile handsets or the fixed mobile stations mounted in vehicles. Mobile stations 102, 104, and 106 typically include radio and processing functions for exchanging voice and data via radio waves with transceivers (TRX's) in base transceiver stations (BTS's) 114 and 116. The transceivers (TRX's) are shown in FIG. 1 as transceivers 114a, 114b, 114c, 116a, and 116b. The BTS's may be thought of, in one sense, as the counterpart to the MS's within the cellular network, and its main role is to connect the mobile stations with the rest of cellular communication network 100.
There is also shown in FIG. 1 a base station controller (BSC) 118, whose function is to monitor and control the BTS's. There may be any number of BSC 118 in a network, whose responsibility includes, among other responsibilities, radio interface management, e.g., the allocation and release of radio channels and hangover management. Mobile Services Switching Center (MSC) 120 controls one or more BSC's 118 and provides the basic switching function within the cellular network, including setting-up of calls to and from the MS's. MSC 120 also provides the interface between the cellular network users (via the BSC and BTS) with external networks (e.g., PSTN or public switched telephone network). The components of GSM cellular network 100 are well known to those skilled in the art and are not discussed in great detail here for brevity's sake. Additional information pertaining to GSM and the cellular networks implementing the GSM standard may be found in many existing references including, for example, Redl, Weber & Oliphant, An Introduction to GSM (Artech House Publishers, 1995).
In the prior art, the radio circuitries of the TRX's are typically implemented such that they co-locate with other circuits of the BTS. By way of example, FIG. 2 illustrates in greater detail exemplary prior art BTS 114 of FIG. 1, including TRX's 114a, 114b, and 114c. As is typical, the antennas of the prior art TRX's co-locate with the BTS such that the BTS defines the cell. Although one antenna is shown to facilitate simplicity of illustration, separate transmit and receive antennas may be provided for each TRX, as is well known. Other major functional blocks of BTS 114 includes ABIS interface 202, which implements the circuitry necessary for interfacing between BTS 114 and its BSC. CPU circuit 204 implements the call processing functions, including for example LAPDm processing, speech framing, channel coding, interleaving, burst formatting, ciphering, modulation, and the like. The architecture of the prior art BTS is well known and is not discussed here in great detail for simplicity's sake.
It has been found, however, that the conventional BTS architecture has many disadvantages. By way of example, the integration of the radio circuitries of the TRX's and the processing circuitries of the BTS in one unit results in a complex and maintenance-intensive electronic subsystem. Yet prior art BTS's are often installed in locations selected primarily for optimum radio transmission quality such as on top of buildings and other outdoor structures instead of ease of access. These locations, being exposed to the elements, are typically hostile to the delicate and complex electronic circuits of the prior art BTS. Accordingly, these factors tend to render the installation, maintenance, and upgrade of prior art BTS's difficult and expensive.
The integration of the radio circuitries of the TRX's in the prior art BTS also limits the flexibility with which the cell can be modified to accommodate changes in capacity. In the prior art, the BTS, which contains the co-resident TRX antennas, essentially defines the cell. Although some cell shaping may be accomplished by, for example, employing directional antennas, the cell is more or less limited by the transmit power of the antennas in the BTS. Scaling the transmit power upward increases the cell size at the expense of capacity since the use of larger cells reduces the ability to reuse frequencies among neighboring cells. Increasing the transmit power also increases the amount of heat generated, thereby reducing the reliability of the circuitries in the prior art BTS unless fans and/or additional heat dissipation techniques are employed.
In view of the foregoing, there are desired improved BTS architectures for overcoming the disadvantages associated with prior art BTS's. In particular, there are desired BTS architectures which offer improved reliability and simplified maintenance, as well as increase the flexibility with which the cell can be modified to accommodate changes in capacity.